Technical Abstract:
Screwworms, Cochliomyia hominivorax, are severe pests that cause myiasis in cattle, wildlife and humans. This insect has been eradicated from the Unites States, Mexico and most of Central America using sterile insect technology (SIT). Efforts are underway to eradicate the fly from Caribbean countries. The continued success of the eradication effort requires periodic development of new strains by adapting wild screwworms to the laboratory rearing environment for use in SIT. Highly contagious viral diseases of livestock, such as foot-and-mouth disease (FMD) and classical swine fever (CSF) are endemic in the areas where screwworms are now endemic. Transporting live screwworms for the purpose of developing new laboratory strains presents the risk that an exotic disease of livestock may be introduced to areas free of these diseases. The purposes of this study were to investigate if screwworms are capable of harboring FMD virus (FMDV) and CSF virus (CSFV) once contaminated through rearing media and to evaluate mitigation strategies for reducing the likelihood of exotic disease agent introduction through the movement of screwworms.
Screwworm larvae were raised at 37°C in rearing media inoculated with FMDV or CSFV. The media contained either 0.1% formaldehyde or antibiotics (Penicillin/streptomycin and Gentamicine) and fungicide (Fungizone) to prevent microbial growth. Samples of insects and media were collected daily and tested for the presence of the viruses by virus isolation and reverse transcription-polymerase chain reaction (RT-PCR). FMDV was detectable for the first three days after inoculation into media containing antibiotics and the fungicide but neither FMDV nor CSFV were detected even one day after inoculation into the media containing 0.1% formaldehyde. No virus was detected by VI or RT-PCR from any larvae raised in rearing medium containing formaldehyde or antibiotics and fungicide. These results indicate that screwworms do not carry FMDV and CSFV when they are exposed through rearing media that was inoculated with the viruses.
Collected samples are being further analyzed.